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EXPERIMENTAL DETERMINATION OF NEUTRON ENERGY SPECTRA IN CONCRETE DUCTS.
NAVAL CIVIL ENGINEERING LAB PORT HUENEME CALIF
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Neutron energy spectra were experimentally determined at various positions in air ducts through concrete. The ducted concrete structures studied were built as model entranceways for protective shelters. The spectra were determined for the case of 14-Mev neutrons impinging on the duct entrance, and were based on activation analysis of threshold foil detectors, foil sandwiches, and bare and cadmium-covered indium foils. The experimentally determined spectra were compared to available spectra calculated by Monte Carlo techniques utilizing the ADONIS computer code. From the spectra the dose was calculated and the results were normalized to the dose in free air at one centimeter from the source. The normalized dose, as a function of distance in the duct from the source, is graphically compared for the several analysis techniques. The data presented demonstrate that it is possible to determine the neutron energy spectrum in ducts by the technique of foil activation. Such determinations are useful during the experimental optimization of the protection factor for the duct in which the inclusion of doors, traps, liners, and special wall materials are considered. The data presented herein form a basis for understanding the effect of duct geometry on the protection factor, that is, the inverse of the dose rate at various positions in the duct normalized to the dose rate at the entrance of the duct. Author
APPROVED FOR PUBLIC RELEASE